1. Field of the Invention
The present invention relates generally to a ramming apparatus and, more particularly, relates to a ramming apparatus having a pneumatically driven percussion piston for driving bore holes in the ground to place, for example, underground cables or wires and lines in the ground.
2. Description of the Prior Art
In conventional ramming apparatus having percussion pistons, as described in German Utility Model 8,700,076, a control device is usually formed by a tubular continuation that extends from the rear end of the percussion piston and a control sleeve that reaches inside the tubular continuation and is supported by an axially running bearing part on an end piece of the piston housing. The control sleeve and the percussion piston with the tubular continuation form a rear pressure chamber that is connected to a source of compressed air by a supply channel formed in the bearing part supporting the control sleeve. The buildup of pneumatic pressure in the rear pressure chamber brings about the forward movement of the percussion piston. When the percussion piston reaches the end of its forward movement and transfers the percussion energy to the housing, radial channels of the tubular continuation of the percussion piston are released by the front edge of the control sleeve, and the compressed air is channeled through these radial channels and through axial channels that are formed in the percussion piston and into a front pressure chamber. The rearward movement of the percussion piston is initiated with the channeling of the compressed air to the front pressure chamber taking advantage of the fact that the effective surface area of the piston in the front pressure chamber is greater than the effective surface area of the piston in the rear pressure chamber. During the rearward movement of the percussion piston, the radial channels of the tubular continuation are temporarily blocked by the control sleeve until the radial channels reach the rear edge of the control sleeve. At this point, the pressure in the front pressure chamber is relieved by the escape of the compressed air through the radial channels as well as the venting channels formed in the end piece of the housing, and a new percussion cycle is initiated.
In these types of prior art ramming apparatus, a reverse drive can be achieved by adjusting the control sleeve with the aid of a high pressure air hose that is connected to the apparatus in a manner such that compressed air is admitted earlier to the front chamber. As a result, the forward movement of the percussion piston is cushioned, and when the percussion piston reaches the end of its rearward movement, it strikes the end piece, and a rearwardly directed impetus is transferred to the housing.
According to German Utility Model 8,700,076, the control sleeve may be adjusted axially using a spindle drive driven by a source of pressurized or compressed air as supplied by a high pressure air hose or compressed air hose. Other apparatus are also known in which the control sleeve may be axially adjusted by pulling or pushing the air hose, with the machine switched off, or in which the control sleeve is provided with clearances that can be brought into a position corresponding to the radial channels of the tubular continuation by turning the control sleeve using a compressed air hose (German Patent Specification 3,104,547).
Of the various types of prior art apparatus, a common characteristic can be drawn between them relating to three sections lying one behind the other in the longitudinal direction: the main section of the percussion piston, a control section, formed by the tubular continuation of the percussion piston, the control sleeve and the bearing part, and finally the end piece of the housing. The main section of the percussion piston must have a certain length in order for an adequate inert mass of the percussion piston to be achieved. The length of the control section is determined by the stroke path of the percussion piston and, if appropriate, by the axial adjusting path of the control sleeve. The end piece of the housing serves for fastening the bearing part and the control sleeve and must be able to withstand the impact of the percussion piston during driving of the apparatus in the rearward direction; however, it nevertheless is weakened by the axial venting channels. Therefore, for reasons of stability, this end piece must likewise have a certain length. For these reasons, conventional apparatuses have a relatively large overall length.